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Message-ID: <543F1B46.2010503@cornell.edu>
Date: Wed, 15 Oct 2014 21:11:34 -0400
From: Ken Brown <kbrown@cornell.edu>
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To: cygwin@cygwin.com
Subject: Re: Crash in g_file_monitor on 32-bit Cygwin
References: <53AB82AB.5000304@cornell.edu> <53ADA5B5.10404@cornell.edu> <53ADAF68.2020703@cygwin.com> <53AEA23A.8030306@cornell.edu> <543D4ED3.6020605@cornell.edu> <543D6BB9.3030009@cornell.edu> <543EA4CD.4090305@cygwin.com>
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On 10/15/2014 12:46 PM, Yaakov Selkowitz wrote:
> On 2014-10-14 13:30, Ken Brown wrote:
>> I stepped into gam_check_not_fat (which I should have done to begin
>> with) and narrowed this down further.  The stack location in question
>> gets clobbered by the call to GetVolumeInformation:
> [snip]
>> Here's the code near the call to GetVolumeInformation, followed by what
>> I think is the relevant disassembly:
>>
>>    if (!GetVolumeInformation (root, volname, MAX_PATH, NULL,
>>                               NULL, NULL, fsname, MAX_PATH))
>>      {
>>        fprintf (stderr, "GetVolumeInformation: %d\n", GetLastError ());
>>        return 0;
>>      }
>>
>>     0x00405b3a <+840>:    movl   $0x104,0x1c(%esp) <<<<<<<<<<<<<<<<
>>     0x00405b42 <+848>:    lea    -0x120(%ebp),%eax
>>     0x00405b48 <+854>:    mov    %eax,0x18(%esp)
>>     0x00405b4c <+858>:    movl   $0x0,0x14(%esp)
>>     0x00405b54 <+866>:    movl   $0x0,0x10(%esp)
>>     0x00405b5c <+874>:    movl   $0x0,0xc(%esp)
>>     0x00405b64 <+882>:    movl   $0x104,0x8(%esp)  <<<<<<<<<<<<<<<<
>>     0x00405b6c <+890>:    lea    -0x224(%ebp),%eax
>>     0x00405b72 <+896>:    mov    %eax,0x4(%esp)
>>     0x00405b76 <+900>:    lea    -0x328(%ebp),%eax
>>     0x00405b7c <+906>:    mov    %eax,(%esp)
>>     0x00405b7f <+909>:    call   *0x41248c    <----- GetVolumeInformation?
>>     0x00405b85 <+915>:    sub    $0x20,%esp
>>     0x00405b88 <+918>:    test   %eax,%eax
>>     0x00405b8a <+920>:    jne    0x405bb5 <gam_server_create+963>
>>     0x00405b8c <+922>:    call   *0x412480    <----- GetLastError?
>>     0x00405b92 <+928>:    mov    %eax,%esi
>>     0x00405b94 <+930>:    call   0x408df0 <__getreent>
>>     0x00405b99 <+935>:    mov    %esi,0x8(%esp)
>>     0x00405b9d <+939>:    movl   $0x40c70f,0x4(%esp)
>>     0x00405ba5 <+947>:    mov    0xc(%eax),%eax
>>     0x00405ba8 <+950>:    mov    %eax,(%esp)
>>     0x00405bab <+953>:    call   0x408df8 <fprintf>
>>     0x00405bb0 <+958>:    jmp    0x406073 <gam_server_create+2177>
>>
>> Note the two marked movl instructions involving 0x104; I guess one of
>> these is the culprit, but I don't really know what's going on.
>
> While it should be purely academic now, the issue might have been a failure to
> mark pGVPN as WINAPI (IOW __stdcall on x86):
>
> -  BOOL (*pGVPN)(LPCTSTR, LPTSTR, DWORD);
> +  BOOL (WINAPI *pGVPN)(LPCTSTR, LPTSTR, DWORD);

Ah, that makes sense.  Thanks.  I'm glad to have an explanation.

Ken

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